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Twenty-five mid-gestation guinea pigs were studied to determine the nature of spontaneous uterine contractures and elucidate the temporal relationship between blood flow and contractile activity. In the first protocol, 15 mid-gestation guinea pigs with indwelling vascular catheters were studied. Blood flows were measured by radioactive microsphere technique during rest, uterine contracture, and, in six animals, 1 minute after contracture activity. During contracture, maternal blood flow to the placenta closest to the electrode fell to 81.3 ± 5.3% of control (n = 15, P ±. 01) and then rose to 130.4 ± 10.2% of control (P ≤. 01) 1 minute after a contracture. The corresponding relationships were also significant for placental vascular resistance and constitute a reactive hyperemic response of the placenta to uterine contracture. No such phenomenon was observed in the more remote placentas on either the ipsilateral or contralateral side.To investigate the nature of contractile activity, electrodes were placed ...

In order to determine the effect of the narcotic analgesic oxymorphone hydrochloride (Numorphan, DuPont) on fetal heart rate (FHR) variability, mathematical indices of short-term and long-term FHR variability were determined continuously from R–R intervals of the electrocardiogram in eight chronically instrumented ovine fetuses for 60 min before and after a maternal intravenous bolus of 0.04 mg/kg oxymorphone. The index of short-term variability decreased from 12.7 ± 2.0 during control to 9.7 ± 1.7 during the period from 10 to 30 min after oxymorphone administration during periods of low-voltage, high-frequency electrocortical activity (LVHF ECoG) (P < 0.05). Mean FHR was decreased from 169 ± 8 beats per minute (bpm) during control to 155 ± 7 bpm 30 to 50 min after oxymorphone (P < 0.05). Fetal electrocortical activity was also determined and the decrease in FHR short-term variability occurred despite an increase in the percent time spent in LVHF electrocortical activity from 53 ± 4% during the control pe...